The present invention relates to safety devices for elevated structures, more particularly, it relates to apparatus to facilitate the evacuation of persons from elevated structures.
Oil and gas drilling rigs and production platforms, by virtue of the volatile, flammable nature of the products with which they deal, are sometimes exposed to explosions and fires. Although the occurence of explosions and fires is infrequent, they present an extremely hazardous situation for personnel on the drilling rig or production platform. Immediate, fast and safe evacuation of personnel is essential to prevent loss of life or limb. When these rigs are located on shore, the majority of the rig personnel is close to ground level and can simply run away from the rig. When drilling, producing or reworking operations are being carried out offshore, the rigs normally are located on an offshore platform. These platforms are usually at a considerable height above normal water level to isolate the platform from the effects of wave action present during rough seas. Therefore, personnel on these offshore platforms have the additional problem of descending to the level of the water so that they can move away from the rig. Merely jumping from the platform is neither a practical nor safe way of evacuating since the impact upon hitting the water could seriously injure the person. Accordingly, many systems and devices have been proposed to provide for the safe evacuation of personnel from an offshore platform during an emergency.
One system which is known to the applicant of the present application is disclosed in U.S. Pat. No. 4,202,427. It comprises an A-frame which is pivotally attached to the rig and, in the standby position, is oriented vertically. A personnel capsule is suspended by a cable from the A-frame. In the event of an emergency, personnel enter the capsule and activate a release mechanism which allows the A-frame to pivot outwardly from the rig to a substantially horizontal position. The capsule then descends at a controlled rate of speed on the cable connected to the A-frame. The number of personnel which can escape in the device is limited by the number which can fit in the capsule.
Another system which has been proposed comprises a flexible chute connecting the platform with a boat. The material used to make the chute is usually either easily melted by intense heat or is flammable, with the result that the chute is burned or otherwise rendered inoperative before it can be used.
U.S. Pat. No. 4,203,504 discloses a system for evacuating personnel from an offshore platform comprising a stable buoyant structure anchored a distance from the platform with cables connecting the structure and the platform. In an emergency situation, rig or platform personnel are evacuated in personnel carriers which descent on the cables from the platform to the buoyant structure. Because this system requires the use of so much auxiliary equipment, such as the buoyant structure and enough personnel carriers to evacuate all personnel which might be on the rig or platform at any given time, it is relatively expensive. Also, the buoyant structure and the cables connecting it to the platform may interfere with boat traffic around the platform and become damaged.
U.S. Pat. No. 3,880,254 discloses three embodiments of a system for evacuating personnel from an offshore platform. In the first embodiment, a boom is pivotally attached at its lower end to the legs of the platform, below the surface of the water. The boom is normally stored in a substantially vertical orientation, with the upper end of the boom adjacent the deck level of the platform. A head is connected to the upper end of the boom, and life lines are connected between the head and the platform. When an emergency situation arises, the boom pivots outwardly from its vertical standby position to a substantially horizontal position in which the head is at a water level. Personnel to be evacuated then descend via the life lines, which extend at an angle from the platform to the head. A disadvantage of this embodiment is that, in the stored position, the boom extends upwardly from below the water line, and is vulnerable to contact with supply boats around the platform, which could damage the boom. Another disadvantage is that flammable lines may burn or melt and steel cables may fray and injure those trying to use the escape device. In the second embodiment, the boom comprises a stairway which is pivotally attached at its upper end to the platform, adjacent the deck level. A buoyant head is connected to its lower end. It is stored, substantially vertically, with the head below water level. When the boom is needed, the buoyant head is allowed to lift the lower end of the boom to the surface of the water. At this time, the boom is at an angle to the vertical. Rig personnel then descend to the water level via the stairs on the boom. In addition to suffering from the first-mentioned disadvantage of the first embodiment, in this embodiment the time for evacuation of the personnel is increased due to the angular orientation of the boom. This added time is particularly disadvantageous in emergency situations when time is of the essence. Also, in their haste to evacuate the platform, the personnel may trip down the stairs and injure themselves. Furthermore, since some of the stairs are stored underwater, sea fauna and flora may attach themselves to the stairs, causing an extremely slippery surface. In the third embodiment, the boom also comprises stairs and buoyant head connected to a lower end of the boom. However, the upper end of the boom is pivotally connected to the platform adjacent the deck level. The boom is stored in a substantially horizontal position alongside the deck level of the platform. When needed, the boom swings outwardly and downwardly from the platform such that the lower end of the boom is adjacent the water level and the boom is at an angle to the vertical. As with the second embodiment, the time for personnel to descend from the platform is increased and there is the danger that offshore workers may trip on the stairs.